In a small bowl, mix together the garlic, thyme, rosemary, salt, and pepper. Rub this mixture evenly all over the chuck roast.

In a Dutch oven or heavy stockpot, heat the olive oil over high heat. Reduce to medium high and add the roast, searing the meat on all sides until golden brown all over, about 4 minutes per side. Remove the roast to a plate and add the onion and fennel to the pot. Cook, stirring often, for 3 minutes or until fragrant.

Deglaze the pot with the red wine and the beef broth and simmer for 2 to 3 minutes, scraping up any brown bits that may have stuck to the bottom. Stir in the marinara sauce. Return the roast to the pot, nestling it into the vegetables. Cover with the lid and place in the oven for 2 hours and 30 minutes, turning the meat once about halfway through.

Remove the lid from the pot and scatter the potatoes around the meat. Return the pot to the oven, uncovered, and cook for another 30 minutes or until the potatoes are cooked through and the meat is tender. Allow the pot roast to rest for 30 minutes before serving.

Reheat the braised fennel and potatoes in the pan juices, then arrange on a platter. Slice the pot roast and serve alongside the vegetables. Spoon some of the pan juices over everything before serving.